1. Field of the Invention
The present invention relates to mixtures of partially crystalline aliphatic polyamides and partially aromatic polyamides, the proportion of aliphatic polyamides being more than 50% by weight, the quantitative ratio of the aliphatic carbon atoms to amide bonds in the aliphatic polyamides being in the range of 8:1 to 12:1 and the partially aromatic polyamides, which are present in deficit, having, in addition to hexamethyleneterephthalamide (6T) units, further partially aromatic and/or aliphatic amide units and being predominantly partially crystalline.
In addition, the invention relates to moulded articles thereof and also the use of these mixtures for producing express couplings or connectors for fuel lines, for fuel filter housings, tank filling connections and vent lines, and also as layer material for single and multi-layer fuel lines.
For producing fuel lines for automotive vehicles, polyamide 11 or 12 have been used practically exclusively for decades. These polyamides were initially processed into simple mono-pipes, which nevertheless soon no longer fulfilled demands due to their high fuel permeability and were replaced by multi-layer automotive vehicle pipelines. Lines of this type have a high thermal loadability, high longitudinal stability and low permeability not only for the main components of the transported fuels, but also for additives and other components which are present therein.
2. Discussion of Related Art
Such lines are described for example in DE 40 06 870 C1, DE 101 10 964 A1, EP 1 077 341 A2, in the German utility model G 92 03 865.4 U1, in U.S. Pat. No. 5,469,892 or in the Japanese published document JP 07-308996. The generality of all the technical solutions, which are proposed there and in further patents, resides in the fact that the pipes are normally constructed at least from three layers which assume different functions. One of these layers functions as a barrier layer and comprises in some cases polymers other than polyamide, for example ethylene/vinyl alcohol copolymers or fluoropolymers which have been made electrically conductive. Furthermore, adhesive layers can be present, if for example the inner layer is not compatible with the barrier layer. Sour gas resistance is required of the inner layer, i.e. high resistance to petrol containing peroxide. The outer layer must finally be mechanically stable, wear-resistant and resistant to zinc chloride.
The possibilities which are offered of improving the properties of fuel lines by the combination of different polymer materials in a composite material are generally not given with material-side optimisation of express couplings or connectors which connect hose or pipelines. Express couplings of this type, as have long proved to be outstanding in practical use, are described for example in DE 37 27 858 C2 and in DE 38 43 995 C2. As a result of the otherwise very expedient construction of these express couplings, it is absolutely impossible to manufacture these from more than one material. Since again only polyamide 11 or 12 are possible for the production thereof, significantly higher fuel permeation through these express couplings must be taken into account, compared to multi-layer pipelines. There has been no lack of attempts to rectify this defect. One of these designs for a new configuration of express couplings is known generally as mono-sandwich technology, a method in which a second material is added in the core region of the connector. This method is however comparatively complex, process control is difficult and can only be mastered by well-trained operators and, in addition, the processing machine is also dearer than a conventional injection moulding machine.
Mixtures of partially aromatic polyamides and aliphatic polyamides are known from patent literature. Thus EP 0 849 746 B1, which relates to the preparation of thermoplastically mouldable magnetic materials, claims “Method for producing a thermoplastically processible moulding compound made of a) 70 to 99% by weight of a partially aromatic copolyamide with a proportion of aliphatic dicarboxylic acids of less than 50% by mol of the entire acid monomers and a melting point of more than 280° C., and b) 1 to 30% by weight of an aliphatic polyamide or copolyamide with, on a statistical average, at least 10 CH2 groups per —NHCO group”. The aliphatic polyamide is hence present in deficit.
A similar polyamide mixture, in which the aliphatic polyamide is contained in deficit, is known from EP 1 245 640 A1.